Many new consumer electronic products, particularly video products, are available with hand held infrared remote control transmitters. A consumer may have separate remote control transmitters for a television, a cable converter, video cassette recorder, and a video disc player, for example. In such a case, it is confusing to know which transmitter to pick up to control which product. Moreover, carrying around four different remote control transmitters spoils the convenience of the remote control feature. It is therefore desirable to provide a single remote control transmitter for controlling each of the several products.
A number of solutions have been proposed for this problem in the prior art. One example is disclosed in the patent to Litz et al, U.S. Pat. No. 4,274,082. In the Litz et al system, an amplifier, a tuner, a tape recorder, and a turntable are interconnected by a two-conductor cable. Each of these devices is controlled by a corresponding microprocessor, and a hand held transmitter is used to transmit coded signals that control the operation of the individual devices. The coded signals are received by a common receiver and first conversion circuit to provide voltage pulses on the two-wire cable. Additional conversion circuits are required for each microprocessor in order to convert the voltage pulses on the two-wire cable to pulses which can be used by the microprocessors.
Another example is disclosed in U.S. Pat. No. 4,200,862 to Campbell et al. The Campbell et al system includes a single receiver/transmitter unit which may be placed on a table, for example, and a hand held transmitter, but in this case, the receiver/transmitter unit injects digital pulses onto the house mains at times of zero crossing of the mains voltage. Various appliances are plugged into the house mains via slave units which are each responsive to an assigned digital address and a digital operation code to control its appliance.
Common to both the Litz et al and Campbell et al systems is the use of a central receiver, an interconnecting transmission line and the requirement of a separate controller device for each product or appliance. Clearly, this approach solves the basic problem of multiple transmitters for multiple products or appliances, but the solution is both complex and expensive from the point of view of the consumer. A simpler, less expensive solution to the problem is needed.